All-Optical Frequency Shifting - Optical Signal Processing by Silicon Photonics - page 85

silicon can be achieved at the cost of very high power intensities but again are not
suitable for nanoscale chips.
Almeida et al. [ 33 ] presented the experimental demonstration of efficient opti-
cal switching in silicon resonant structures (Fig. 4.3 ) by strong light-confining to
enhance the sensitivity of light to small changes in refractive index. They claimed
that the transmission efficiency of the structure can be modulated by up to 94 % in
less than 500-ps of switching time using light pulses with energies as low as 25 pJ.
They used ring resonator of 10 μ m diameter, while both the silicon waveguide and
the ring resonator are channel waveguides with 450-nm-wide by 250-nm-high rec-
tangular cross-sections.
Michael Forst et al. demonstrated high-speed all-optical switching via verti-
cal excitation of electron-hole plasma in oxygen-ion implanted silicon on insula-
tor micro-ring resonator. The spectral response of the device is rapidly modulated
by photo-injection and subsequent recombination of charge carriers at artificially
introduced fast recombination centers, at an implantation dose of 1 × 10 12 cm − 2 .
The carrier's lifetime is reduced to 55 ps, which facilitates optical switching in the
1.55 μ m wavelength range at modulation speeds of more than 5 Gbits/s [ 34 ].
Jeffery J. Maki reported optical switches; one consisting of two waveguides
crossing each other at an angle to form an intersection, and a pair of electrodes
placed within a proximity of the intersection to switch a light traveling from the
first waveguide to the second waveguide. This intersection includes a geometry
that supports single and multimode propagation (the intersection includes a geom-
etry having a ridge width ranging approximately from 2.6 to 19.2 μ m and a ridge
height ranging approximately from 4 to 16 μ m) [ 35 ].
In [ 36 ] a waveguide-type optical switch based on amplifier is disclosed, which
amplifies an optical signal passing through this waveguide (by performing an opti-
cal pumping through a WDM optical coupler in the said optical waveguide, com-
prising a fluorescence emitting electro-optic material), and at the same time carries
out an optical switching by using an optical waveguide refraction index change
induced by an electro-optic effect under an electrical control (Fig. 7.4 ).
Fig. 7.4 Silicon resonant
structure [ 32 ]